Priming device



Dec. 25, 1956 R. G. GUENTER PRIMING DEVICE Filed Dec. 5, 1952 RICHARD e.GUENTER INVENTOR.

AGENT.

PRIMING DEVICE Richard G. Guenter, Lawrence, Kans., assignor to HerculesPowder Company, Wilmington, Del., a corporation of Delaware ApplicationDecember 3, 1952, Serial No. 323,856

8 Claims. Cl. 102-27 This invention relates to detonating means forexplosive charges and in particular to detonating devices especiallyadapted for use in applications where relatively insensitive explosiveis employed, or where advanced temperatures are encountered which renderthe use of conventional blasting initiators undesirable.

In recent years there has been a trend toward the use of relativelyinsensitive blasting agents which contain little or no nitroglycerin anddepend primarily for explosive trength upon such materials as ammoniumnitrate. While these blasting agents when brought to detonation arecharacterized by suflicient strength for most blasting operations, theyare normally not detonatable by commercially available blasting caps. Infact, the test employed to determine the sensitivity characteristics ofsuch blasting agents is usually one in which their resistance todetonation by a No. 6 or No. 8 cap is determined.

The usual methods for detonating these explosives have involved the useof separate priming cartridges of high explosive such as tn'nitrotoluene(TNT) which are brought to detonation by means of commercial electricblasting caps. is employed which contains a base charge of about 1030 g.of pentaerythritol tetranitrate or equivalent explosive. While both ofthese means of initiating explosives are operable, they stillnecessitate the use of blasting initiators which are expensive and whichare themselves considerably more sensitive to both heat and shock thanthe blasting agent itself. Thus, the safety for which the insensitiveblasting agents were originally designed is still not always obtainablein the degree desired by the art.

Special difficulties are encountered in shooting hot holes in which thetemperatures often reach a point high enough to cause prematuredetonation of conventional' blasting caps. A means for initiating theseinsensitive explosives which does not require the presence of largeamounts of sensitive explosive or electric blasting caps in the boreholeitself is therefore greatly to be desired.

Now in accordance with the present invention, there has been developed ameans for initiating insensitive blasting agents and explosivesgenerally which does not require the presence of either highly sensitivehigh explosive compositions or electric initiators of any sort in theimmediate vicinity of the charge to be detonated.

Generally described, the present invention is a priming device fordetonatable explosive compositions which comprises a detonatable body ofcompacted explosive composition containing crystalline high explosiveselected from the group consisting of cyclonite (RDX) andpentaerythritol tetranitrate (PETN) and at least of nitrocellulose. Inaccordance with one embodiment of the invention, the compacted body isassociated with detonative means. Preferably, the detonative meansAlternatively a highly potent booster cap' atent PETN or RDX coveredwith fabric or plastic) or Cordeau (granular TNT covered with thin leadtubing containing the desired number of grains of explosive pe foot andwill be disposed in detonating relationship wit the explosive body.Preferably, the fuse will be di: posed in a recess, that is, in a Wellor a perforatio formed in the compacted body, although other suitabldisposition may be employed. In applications where rt sistance to heator shock is not an important facto: blasting caps may be similarlyemployed as the detonz tive means. In a preferred embodiment of theinvei tion, the compacted explosive body is formed into a axiallyperforated cylinder, the perforation extendir through at least a majorextent of the length of th cylinder. With such a structure, thedetonative mear employed may be disposed in or pass through the pe:

. foration.

The compacted body of explosive compositionin a cordance with thisinvention is readily detonated t detonating fuses of the desiredstrength, such as Prim: cord and Cordeau, but is highly insensitive bothto shoc conditions which can normally be expected during blas ingoperations and to. ignition or detonation by temper: tures usuallyencountered. It is usually desirable to i] corporate a small amount ofstabilizer for nitrocelh lose, such as diphenylamine or Centralite, inthe con positions from which the compacted body is forme The amountemployed is usually in the order of .2 to .19 While this compositionwill normally be sufiiciently w; ter resistant for most moistureconditions encountere it is desirable in some instances to include anon-vol; tile plasticizer for nitrocellulose such as diethyl phthalatdibutyl phthalate, dimethyl phthalate, ethyl Centralit ordinitrotoluene. While varying amounts of the plasi cizer may beemployed, increase in plasticizer e fects a corresponding decrease insensitivity to de onation It has further been found that nitroglycer canbe employed in amounts up to about 5% WithOl adversely affecting thethermal stability of the OV612 composition. In general, it has beenfound that it unnecessary to employ more than 5% of plasticizer Sll1(this amount has been found to render these compositior sufficientlyresistant to water that they will shoot wit 50 grain Primacord (50 gr.PETN per foot) after daj of exposure to water at pressures as high as p.s. When employed in hot holes, the compacted bodi primed with Primacordhave been found to function pro; erly without violent decomposition orpremature e1 plosion at temperatures of 500 to 1000 F.

The compacted bodies are preferably made in coaxia ly perforatedcylinders by extrusion 'in accordance Wi' known smokeless powderextrusion techniques. Ho ever, the compacted bodies may have any desiredsha and may be molded by any desired process.

Having generally described the invention, several er bodiments will bemore specifically illustrated with re erence to the accompanyingdrawings in which Fig. represents a longitudinal section of acylindrical cor pacted body in accordance with the invention; Fig. is asectional end view of Fig. 1; Fig. 3 is a part elev tional, partsectional view of the body of Figs. 1 a1 2 primed with detonating fuse;Fig. 4 is a part section: part elevational view of an explosivecartridge priml with the device of Fig. 3; Fig. 5 is a part sectional,pa elevational view of a cylindrical compacted body prim with anelectric initiator; and Fig. 6 is a side elevation a borehole primed inaccordance with the invention.

Referring now to the drawings in which like numbe represent similarparts, and particularly to Figs. 1 to a cylindrical compacted body 10 ofexposive compo: tion in accordance with this invention is provided wi acoaxial perforation 11. Alength of detonating 11 12 is passed throughthe coaxial perforation 11 of tl ady 10 and is suitably secured therein.In Fig. 3, the etonating fuse is secured within the perforation by reamsof a knot tied in the detonating fuse which pre-- :nts its withdrawal..In Fig. 4, a cartridge 13 of insensitive explosive 1s nipped with acoaxial bore 14 defined by a hollow tube 5 passing concentricallythrough the cartridge 13. The )llow tube is indented at 16 to provide adetent means. concentrically perforated, compacted body of explosiveaccordance with the invention is disposed in the coial bore 14 and isprevented from passing therethrough the indentation 16 in the tube 15.Detonating fuse 12 .sses through the compaetedbody and extends cometelythrough the coaxial bore .14 :of the cartridge 13.

4 t be detonated at a safe distance from the borehole 23 by means of anelectric initiator.

The following examples are presented to more specifically illustrateembodiments of the invention. In the table, Examples 1 to 24 illustratedifferent compositions for the compacted body. The water resistance ofthese compositions and the comparative sensitivity to detonation of Wetand dry compositions are set forth. The compacted bodies tested were inthe form of coaxially 10 perforated cylinders 4 inches in length and0.67 inch in diameter. The diameter of the perforation was about 0.27inch. These cylinders were prepared by conventional smokeless powdercompounding and extrusion techniques as hereinafter described. Allcompositions were stabilized he leading end of the detonatig fuse 12passed 15 with 0.3 of diphenylamine.

Primacord Sensitivity 1 Explosive, Percent 15;, Dry Wet-45 'Lbs.Pressure for 5 Days Water RDX PET-N NO Plasticizer Gr. Gr. Gr. 60 Gr.100 Gr. Pickup}; 30 Gr. 40 Gr. 50 .Gr. 60 Gr. 100.61.

percen 19. 7 0 DEP. S 12.25 F F PS PS S 19. 7 1 DEP- PS 7. 90 F F PS PSS 19. 7 2* DEP. PS 6. 5,2 F F PS S 19. 7 3 DEP- F 4. 67 F F PS 19. 7 4*DEP F 1. 50 F PS S 19. 7 5* DEP. F 0. 74 F F PS 19. 7 6* DEP. F 0.00 F FF 15. 7 4 DEP. F 1.16 F PS PS 10.7 4 DEP. F 5.19 F F S 24. 7 0 PS 11.87F F PS 20.7 4DEP F 1.38 F F PS 19.7 5N.Ge PS 0.52 F PS S 19.7 5 DNT-F 1. 29 F PS 19. 7 5 TNT F 1.07 F -]?-S 19. 7 S 8.03 S 19.7 1* DEP S 9.96 PS PS '19. 7 2* DEP- S 10. 10- PS PS 19. 7 3* DEP. S 9. 77 PS PS 19.7 4* DEP. S 3.88 PS S 19.7 5 DEP- S 1. 90 PS -S 19.7 6 DEP- S 1.57 S 24.7 S 5.15 PS S 29. 7. .0 S 5.09 F PS 16. 7 3 DEP. S 11.01 F PS 1 Testedby shooting with PETN Primacord 01 indicated strength. RDX-eyclonite.PETN-pentaerythritoltetranitrate. N Cnitrocellu10se.

DEF-diethyl phthalate.

N G-nitroglycerin. DNT-dinitrotoluene. TNT-trinitrotoluene.

S-'-sh'ot,hole in plate.

PS-shot, dent inplate.

*Plasticizer added to composition.

ough a centrally orificed-wooden'disk 17 which has a meter greater than'thatof the tuber15. The leading i of the detonatingrfuse 12 is knottedto :prevent its isage through the disk 17. The priming cartridge 13 vybe lowered into a'borehole by means of the detonatfuse 12 and thecompacted'priming body 10 is thus intained imposition in thecentralportion of the carle 3- n Fig. 5, a cylindrical, compacted .body 18 inaccord- :e :with the invention is provided with a well19. An ctricinitiator 20 is disposed in the well '19 and con- :ted to a currentsource (not shown) lay lead wires 21. n Fig. 6, blasting cartridges 22are disposed in a verti- .borehole.23. The lowercartridgeZZ is primedinacdance with the invention-by disposing a coaxially peratedcylindrical body 10-of explosive composition, as wn in Fig. l, in theupper portion of the cartridge. A gth of Primacord 12 passes-laterallythrough the carlge and-through the coaxial perforation of the comtedbody 10. The Primacord 12 is then tied as shown [.leads out ofthe'borehole. The -:remaining cartridges aredisposed .ontopof the-1ower:primed cartridge. The e hole is "stemmed as at 25. 'The'Primacord12 may Example v25 Field trials were conducted in'which severalboreholes were loaded with commercial blasting cap insensitive blastingagent principally comprising ammonium nitrate. The temperature in theseboreholes was between 400500' F. due to undergroundfires. In each hole aprimer cartridge was employed similar to that shown in Fig. 4. Theprimer cartridge contained commercial blasting cap insensitive blastingagent. The compacted body was similar to that of Example 1 and contained80% RDX, 19.7% NC, and 3% diphenylarnine. A 50 grain PETN Primacord wasemployed which was initiated at a distance from the hole by means of anelectric blasting cap. After being loaded, the .holes were not fired forabout '20 minutes. All holes fired normally and with no indication ofany decomposition of the compactedbody in the primer cartridge.

From the foregoing examples, and especially from Examples l to 24, itwill be seen that the compositionof the compacted bodies may be subjectto considerable variatron. It'hasbeen found, however, that at least 15%of nitrocellulose must be employed in order to obtain a compacted'bodyhaving the requisite physical strength and to obtain the necessaryextrusion characteristics. When less than 15% of nitrocellulose isemployed, the bodies do not compact well and are crumbly.

The amount of crystalline explosive employed will depend on the degreeof sensitivity required for the particular application. Due to the factthat PETN is more sensitive to detonation than RDX, less PETN than RDXneed be used with a detonating fuse of a particular strength. Similarly,the amount and nature of the plasticizer may be varied to give thedesired characteristics in terms of water resistance and sensitivity toheat and shock. For commercially available detonating fuse, it has beenfound desirable to employ at least 75% of RDX and at least 70% of PETN.

While cylindrical compacted bodies of RDX or PETN with nitrocellulosehave been employed to specifically illustrate the invention, theinvention is not so limited, since as previously indicated the compactedbodies may be of any desired shape.

The compacted bodies are easily produced by the usual smokeless powderprocess. In accordance with the preferred process, the nitrocellulose,Wet with 2B alcohol, is placed in a sigma-blade mixer together with thestabilizer and plasticizer, if used, the particulate explosive, acetone,and additional 2B alcohol. The ingredients are then thoroughly mixed,preferably for about 3 hours. In accordance with the preferredprocedure, the composition is then extruded through a die of the desireddimensions, the perforation being formed by a die pin of a size slightlylarger than the detonating fuse to be employed. The compacted, extrudedbodies are dried in air at a temperature of about 120-140 F. to effectsolvent removal. Alternatively, however, the paste from the mixer may becompression molded in a suitable mold and the solvent removed by dryingas before. The RDX or PETN employed should be finely divided.

From the foregoing, it will be seen that the priming devices of theinvention have many advantages. Devices having high heat or shockresistance may be prepared which when detonated, are highly bn'sant andcapable of satisfactorily initiating insensitive blasting agents orother explosive composition. While the compacted bodies may be made inany size, small, inexpensive bodies are satisfactory. These bodies arestructurally self-suflicient and require no metal or plastic shells forsupport. What is of great importance from the standpoint of bothmanufacturer and user is that the compacted bodies can be easily andeconomically prepared by utilizing known smokeless powder extrusiontechniques and equipment. Other advantages will be apparent to thoseskilled in the art.

While the explosive priming device of the invention will have primaryutility when used with the currently popular insensitive blastingagents, the device can also be used with more sensitive explosives ifdesired. In like manner, although the device has special utility forshooting hot holes, its use is not so restricted. It is intended thatthe scope of this invention be defined solely by th scope of theappended claims.

What I claim and desire to protect by Letters Patent is 1. As a newarticle of manufacture a priming devic for detonating blasting chargescomprising a compacte explosive composition formed as a cylinder, thewalls 0 said cylinder forming an annulus about a substantiall coaxiallydisposed perforation extending through at lea: a major extent of thelength of the cylinder and adapte to contain a detonating means, saidexplosive consistin essentially of at least 75 percent cyclonite and atleast 1. percent nitrocellulose to form an independent cohesiv body.

2. An article of claim 1 wherein said perforation ex tends through saidcylinder.

3. An article of claim 1, wherein said detonating mean is a detonatingfuse disposed in at least a portion of sait perforation in propagatingrelationship with said com pacted composition.

4. An article of claim 1 wherein the said compacte explosive containsnot in excess of about 5 percent of nonvolatile plasticizer fornitrocellulose.

5. As a new article of manufacture a priming devic for detonatingblasting charges comprising a compacte explosive composition formed as acylinder, the walls 0 said cylinder forming an annulus about asubstantiall coaxially disposed perforation extending through at lea: amajor extent of the length of the cylinder and adapter to contain adetonating means, said explosive consistin, essentially of at leastpercent pentaerythritol tetrani trate and at least 15 percentnitrocellulose to form a1 independent cohesive body.

6. An article of claim 5 wherein said perforation ex tends through saidcylinder.

7. An article of claim 5 wherein said detonating mean is a detonatingfuse disposed in at least a portion of sait perforation in propagatingrelationship with said corn pacted composition.

8. An article of claim 5 wherein the compacted ex plosive contains notin excess of about 5 percent of nonvolatile plasticizer fornitrocellulose.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain Feb. 16, 1932

